In the formation of electrical connections it has been customary to strip insulating material from the end of an electrical conductor, then to enclose the stripped wire ends in an electrically conductive metal ferrule or barrel to which a terminal contact or some other conductive member is or can be connected. Compression force is the applied to the barrel to press and permanently deform it into an electrically conductive and mechanically strong connection with the wire ends contained therein, known as crimping. It is also known to enclose the metal barrel in a sleeve or shell of insulating material prior to or after crimping.
There have been numerous approaches to the applying of the compression force, beginning with a simple flattening, or a dimpling. Most approaches use a pair of opposing dies, sometimes one of which is called a punch and the other an anvil. The shape of the dies or one of them has been varied to provide a crimped connection having a distinct cross-sectional shape; for instance, see U.S. Pat. No. 3,098,517 (oval shape), U.S. Pat. No. 2,359,083 (diamond shape), and U.S. Pat. No. 2,693,216 ("W" shape).
More complex crimping has been used, such as is disclosed in U.S. Pat. No. 2,816,276 where several crimp indentations are applied to the same connection by separate dies at different locations around the circumference of the barrel, each being distinctly skewed to partially wrap around the barrel. A single but progressive crimp is disclosed in U.S. Pat. No. 2,952,174. Crimping force may be applied from three directions around the barrel as in U.S. Pat. No. 2,965,147.
A particularly effective crimp which has been popular for many years is formed by four crimping dies disposed 90.degree. to each other, each of which indents the electrical connection directly towards the center of the connection, all simultaneously, to form a four-indent crimp such as illustrated in U.S. Pat. Nos. 4,120,556 and 2,226,849. When an appropriate size of barrel is used with a particular size of conductor, such a four-indent crimp gives excellent electrical engagement among the wires and between the metal barrel and wires, and also gives excellent mechanical engagement and particularly good resistance to torsional stress or twisting because of the four indented areas and four lobes.
The main objective of crimping is to form an intimate electrically-conductive connection of the wire ends to the metal barrel in a manner which is also strong enough mechanically so that the barrel is firmly attached to the wires to resist being inadvertently pulled off.
The primary deficiencies in crimping are that the wire ends can be broken or otherwise damaged if too much compression force is used, or that the wire ends may have spaces between themselves and the barrel, or among themselves or both if enough compression force is not used or is not applied at the optimum location or locations around the circumference of the barrel. Another deficiency in crimping is that substantial axial elongation could occur in the connection; that is, when the metal of the barrel and/or the wires is compressed greatly enough, it flows along the axis of the connection towards the terminal and towards the wire cable. This is especially undesirable in power conductors.
Also, another drawback can be that during the crimping the metal of the barrel may flow through a gap between the lateral edges of the dies as they close toward each other; or localized thinning of the barrel wall may occur, and particularly in thin-walled barrels even shearing of the wall could possibly occur.
A further important consideration is that a seemingly successful crimp which remedies all the deficiencies stated above and achieves high electrical conductivity and mechanical strength and excellent resistance to torsional and tensile stress and to atmospheric corrosion of the barrel and the wire ends, may not be easily or economically adaptable to mass production techniques because more than two dies are required for a single crimping operation. It is highly desirable to utilize fully automated crimping machines (or terminators) having automated feeding of terminals and wire ends to be connected and crimped. Some successful crimps are presently only appliable by the use of hand tools, and some others require manual feeding in semi-automatic production.
In selecting a terminal contact for any particular size of electrical conductor, it would be preferable to select that contact having a barrel size just large enough for the stripped wire ends of the conductor to be inserted without individual outer strands snagging the end of the barrel wall, fraying and not entering inside the barrel. To use a barrel which has an inner diameter much larger than the thickness of the stripped conductor would mean that there would be excessive space between the barrel wall and the wires would have to be eliminated to obtain a crimped electrical connection having satisfactory mechanical engagement and good electrical conductivity. But to have one size of barrel for each size of conductor presents a serious inventory problem also considering the various kinds of terminal contacts, and it is commonly accepted practice to use one barrel size for two adjacent conductor sizes, such as a No. 8 size barrel for both No. 8 and No. 10 sizes of conductors. A No. 8 size barrel matches a No. 8 size conductor, but is oversized for a smaller No. 10 conductor. To overcome this oversize problem, sometimes an intermediate metal sleeve is placed around the wire ends and inside the barrel. Without such a sleeve standard crimping techniques including the four-indent crimp do not provide a satisfactory crimp especially for a many-stranded conductor, because significant voids and spaces remain either among the wire ends, or between them and the barrel wall.
It is one objective of this invention to achieve a crimp which presses stripped wire ends into an optimum level of electrically conductive engagement with a metal barrel and which provides a sound mechanical connection between the wire ends and the barrel so that no disengagement due to tensile strain occurs during normal handling and under normal service conditions for the contact terminal.
It is another objective that a cross-sectional geometry of the crimped connection be obtained which reduces the effects of torsional stress or twisting upon the wire with respect to the connection (which if the wire would be allowed to turn would tend to wedge or cam open the crimp in the barrel) during normal handling and under normal service conditions for the contact terminal, which could lead to degrading of the electrical conductivity or even to mechanical disengagement of the wire from the barrel.
It is yet another objective of this invention to minimize voids or air spaces in the crimped connection to enhance its corrosion resistance and reduce localized overheating and loss of power, while minimizing axial elongation in the connection, and does not break or otherwise damage the individual wire ends.
It is a further objective of this invention not to create thin areas in the barrel wall, nor shear or otherwise damage the barrel or its plated surface.
It is further objective of this invention to provide a method of crimping whereby a successful crimp of a relatively oversized barrel to a conductor can be easily obtained without placing an intermediate sleeve therebetween.
It is yet a further objective to provide a successful confined crimp, that is, confining the sides of the connection during crimping to a width not larger than the original outer diameter of the barrel.
It is a further important objective of the invention to provide a crimp which satisfies all of the above objectives and lends itself more to being easily and economically appliable by means of a fully automated terminal and wire feed and crimping apparatus by requiring only two opposing dies.